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In this work, the production of tributyl citrate via catalytic and self-catalyzed esterification of citric acid with 1-butanol was studied. Both, methanesulfonic acid (MSA) and Amberlyst 70 ion-exchange resin were evaluated as catalysts in the reaction. The kinetic effects of the temperature (353–393 K), the feed molar ratio of alcohol to acid (8:1 to 16:1), and catalyst loadings (0.5–1.5 wt % of MSA, and the equivalent amount of Amberlyst 70) were evaluated. Experiments were carried out using stirred batch reactors under isothermal operation. A Box–Behnken design was used to optimize the number of experiments required to obtain a valid kinetic model. Chemical equilibrium conditions were evaluated independently from kinetic experiments, reducing the number of parameters to adjust during data regression. Self-catalytic rate of reaction was also evaluated, and it was included within the overall kinetic model. The obtained models show good agreement with experiments, and they can be used for process analysis and simulation.

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This work focused on the development of the phase equilibria models required to describe the behavior of mixtures involved in the synthesis of tributyl citrate (TBC) via esterification of citric acid (CA) and butan-1-ol (BuOH). Vapor−liquid equilibrium (VLE) for the mixture TBC−BuOH, liquid−liquid equilibrium (LLE) for the ternary mixture TBC− H 2 O−BuOH, and solubility data for the mixture CA−BuOH−TBC were measured at different temperatures. The thermodynamic consistency was verified with the Wisniak test for VLE data, and the LLE data exhibited linear behavior in an Othmer and Tobias plot. Anhydrous citric acid was characterized by differential scanning calorimetry exhibiting a melting point of 424.9 K, an enthalpy of fusion of 59.2 kJ/mol, an average heat capacity of 255.48 J/mol•K in the evaluated temperature range (320−375 K), and a change of heat capacity from solid to liquid of 236 J/mol•K. Together with reported equilibrium data from the open literature, and the evaluated physicochemical properties, the measured equilibrium data were regressed with the UNIQUAC equation to fit the binary interaction parameters of the components in the mixture. The obtained model agrees well with the whole set of experimental data and can be used for further process design.

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Dibutyl citrate (DBC) was synthesized via partial esterification of citric acid (CA) with n-butanol (BuOH) and characterized for the first time. Then, the monoacid diester was isolated from the reactive mixture by using a pH-controlled solvent extraction procedure. The identity of the obtained product was verified by NMR spectroscopy, finding that it corresponds to a mixture of asymmetric and symmetric isomers. The obtained product was characterized by thermogravimetric and differential scanning calorimetry analysis and by density and viscosity measurements. As per the calorimetric analysis, DBC exhibited a crystallization point below 213 K, a decomposition temperature of 541 K, and an average heat capacity of 2.461 kJ/kg K in the evaluated temperature range (320–375 K). The average liquid density and viscosity in the studied temperature interval (298–313 K) were 1.122 g/cm3 and 2.03 Pa·s, respectively. Additionally, isothermal vapor–liquid equilibrium data (P–x) in mixtures containing the obtained DBC and BuOH were measured at 313, 323, and 333 K. Experimental data were used to fit UNIQUAC interaction parameters for the binary DBC–BuOH. The regressed model showed good agreement with experimental results, making it suitable for further process design and simulation. The obtained data can be used in the development of processes for citrate plasticizer production and in the development of separation processes for DBC.

This work describes the conceptual design and a pilot-scale validation of a reactive distillation column for tributyl citrate (TBC) production by esterification of citric acid (CA) with n-butanol (BuOH). The conceptual design was carried out using novel reactive residue curve maps for mixtures of six components. Subsequently, a computational sensitivity analysis based on validated kinetic and phase equilibrium models enabled identifying critical design and operating variables to assess during experiments. Further pilot-scale experiments were performed according to a Box–Behnken design. The highest productivity at the pilot scale was obtained for a reflux ratio of 0.17, a CA/BuOH mole ratio of 1:13, and a feed flow of the reactive mixture of 4.9 kg/h. These conditions resulted in a CA conversion above 98.8%, a TBC yield of 52%, and a productivity of 24.4 kg/h/m3. It was verified that the process can successfully operate with azeotropic BuOH as feedstock and a prereactor, improving selectivity toward TBC.